1. Field of the Invention
This invention relates to a novel melt transfer web employing a pair of cooperating polymeric coatings capable of releasing a pre-printed graphic pattern from a suitable substrate, transferring the pattern to a workpiece, and permanently bonding the pattern to the workpiece. It relates particularly to a melt transfer web in which hot pressing is employed to decorate or print the surfaces of workpieces comprised of natural or synthetic fibrous materials as well as almost any other porous, semi-porous or non-porous structures.
2. Description of the Prior Art
In prior art melt transfer systems, it is well-known to print a pattern with printing inks having a thermoplastic binder onto paper and then transferring this assembly onto a fabric under heat and pressure. Various releasable layer compositions have been configured to develop efficient graphic pattern transfers onto fibrous or textile material workpieces without damaging physical properties, feel, and touch of the fabric. Such systems were developed in an attempt to overcome the problems associated with satisfying temperature requirements which may vary over a wide range as well as to accommodate the various steps of forming the transfer paper and of performing the heat transfer itself.
One such transfer printing system for providing natural or synthetic fabric material with suitable patterns is described in U.S. Pat. No. 3,918,895 dated Nov. 11, 1975. The patent describes a transfer paper formed by: (1) coating on an optional support, a releasable layer comprising a pasty composition of a high melt-point resin and a solid solvent, the solvent being solid at room temperature and liquid at elevated temperatures where it is capable of dissolving the resin therein; and (2) then printing a pattern, using an ink composition containing a dye or pigment, on the releasable layer.
The patent then describes the transfer of the printed pattern to a fibrous material workpiece which is achieved by: (1) bringing the printed surface of the transfer paper into contact with the workpiece; (2) heating the assembly under pressure; (3) subjecting the workpiece to a dyeing treatment to cause the dye to be absorbed into the fibers of the workpiece; and (4) then subjecting the workpiece to a soaping treatment in order to remove the releasable ink-carrying layer, excessive ink and ink vehicle. If the printed pattern were to be transferred onto the fibrous workpiece by the above heat transfer treatment and the subsequent dyeing treatment not performed, the ink would be left in a sticky state on the surface of the workpiece which is undesirable. Accordingly, it is essential to provide the dyeing treatment as described in the patent to fix permanently the pattern on the fibers of the workpiece.
As is apparent from the foregoing description, the transfer printing system of the cited patent does not permit transfers to workpieces constructed from non-absorbent materials. Also, it is necessary to perform a soaping treatment to remove the transferred releasable coating and excess dye materials. The process as described in the patent thus requires both dyeing and soaping steps to be performed satisfactorily.
Another prior art system for melt transferring inked patterns to workpieces is described in a British Pat. No. 1,393,992 dated May 14, 1975, a corresponding Canadian Pat. No. 1,002,818 dated Jan. 4, 1977 and a corresponding U.S. Pat. No. 4,037,008 dated July 19, 1977. In these patents, a process for producing a flexible transfer lamination is described which is accomplished by: (1) applying a flexible transparent layer of a plastisol ink on a temporary backing sheet by a silk-screen printing method; (2) printing a flexible image layer with lithographic process ink to define an image on the first layer; and (3) applying a flexible plastisol adhesive layer to the image layer so that the three layers form a transfer lamination which can be adhesively applied to a flexible workpiece as a complete unit.
Such a product is suited only for transfer applications to fabrics of cotton and fiber blends which are relatively smooth. The process is not suited for applying patterns to fabrics such as terry cloth toweling or athletic socks. Moreover, plastisols and plastisol inks are not commercially used on nylon and other thermoplastic synthetic fabrics because plastisols will not adhere well enough to withstand washing and abrasion in use. Also, when printing with the flexible transfer lamination described in these patents, the workpiece must be cooled to allow the plastisol to solidify before the base sheet is removed. This involves a cooling step which is undesirable in situations where high productivity is wanted.
A further prior art product which uses polymer-coated transfer paper for hot-melt transfer of graphic patterns may be found in a product buyers guide provided by Kimberly-Clark Corporation describing TRANS-EZE.TM. 3000 heat transfer paper. Such paper has properties which permit lithographic, silk screen, flexographic, rotogravure, letter press, web-fed or sheet-fed offset printed patterns to be transferred to nylon, synthetic, nonwoven, and natural fabric articles. TRANS-EZE 3000 has a plastic-like surface coating which provides the printing and heat transfer surface. The plastic-like surface also serves as the transferable layer which softens during the heat transfer process and returns rapidly to the normal pliable plastic-like surface during the cooling step. In order to accomplish transfer, stripping of the base sheet while hot is required.
Such transfer paper can be used readily to effect heat transfers of patterns to porous woven or non-woven fabrics of natural or synthetic fibrous material such as 100% cotton, polyester blends, wool, nylon and synthetic non-wovens as well as porous poster boards, artificial leather, cork and the like. Fabrics, thus printed, still have good "hand", i.e., feel, and touch, and breathability while retaining good washability. However, this transfer paper does not produce a highly durable image on cotton fabrics which may be laundered to remove soil.
Another prior art transfer paper product is described in British Pat. No. 1,523,869 published Sept. 6, 1978. In that patent a transfer paper system is described which teaches sandwiching the printed characters to be transferred between two continuous polyurethane resin layers carried on a support so that upon heat transfer a bonding and a protective layer for the characters will be provided. However, the heat transfers in accordance with this transfer paper system are limited to applying labels to flexible articles and in particular textile materials.